Research On Polarizing Properties And Sensing Applications Of Graphene-microfiber Hybrid Waveguide

As an important branch of the field of sensing and measuring, optical fiber sensing technology has been one of the hot issues in the science research all over the world. Especially in the fields like biomedical science, precision chemistry, aviation and space industry and environment monitoring, which are harsh on the sensing accuracy and response speed, optical micro-scale sensing technology with the abilities of anti-electromagnetic interference and molecule level sensitivity has been a pivotal scientific problem that needs to be solved instantly, while a huge challenge is in front of us.Microfiber sensors based on surface wave enhancement is one of the important directions in the development of optical micro-nano sensors, which can greatly improve the performance of optical biochemical sensors, realizing the detection with high sensitivity and ultra-short response time in molecule level, as well as the measurement of multiple-parameters. The discovery of graphene material provides a totally new method to the research on the enhancement of optical surface wave and the control of polarizing state in microfiber waveguide, which can realize optical sensing with high sensitivity. As an ultra-thin waveguide structure, graphene has anisotropic propagation constant and the difference of internal energy state can lead to exactly different properties. The Femi energy level of intrinsic graphene is close to the Dirac point, thus the surface wave with TE polarized mode is supported.In this thesis, microfiber and graphene film are combined, evanescent wave is coupled onto the surface of graphene waveguide and transmitted along it, when gas molecules contact the graphene material, the effective refractive index of graphene-microfiber hybrid waveguide structure is changed and a polarizing related attenuation of the transmitting surface wave is caused, the sensing of biomedical gas could be achieved by detecting the intensity of output optical signals; when the contacting length between microfiber and graphene film changes, the transmitting modes of evanescent wave are influenced and the transmitting phase is changed as well, the refractive index of the hybrid waveguide can be determined by designing an interference based system and monitoring the shifts of wavelength, after which the complex refractive index of graphene waveguide can be determined.Firstly, this thesis researches on the properties of monolayer graphene film and microfiber, the introduction of the optical and electrical properties of graphene and microfiber in theory and simulation does foreshadowing for the research on the properties of the entire graphene-microfiber hybrid waveguide theoretically, then we research on the polarizing properties of graphene-microfiber hybrid waveguides, according to the binding mode between monolayer graphene waveguide and microfiber, the polarizing principles and the sensing properties of graphene-attached microfiber hybrid waveguide structure are researched.Secondly, this thesis presents a detailed explanation on the preparation and characterization methods of monolayer graphene film, and the drawing of microfiber is presented, which is a reference for the processing technique of graphene-microfiber hybrid waveguide.Finally, this thesis puts forward confirmatory experiments according to the different sensing applications of graphene-microfiber hybrid waveguide structures, including gas sensing experiments and refractive index sensing experiment. The polarizing control property and the effectiveness on sensing applications of graphene-microfiber hybrid waveguide are verified by the experiments, as well as the graphene-microfiber hybrid waveguide’s ability to realize the molecule level sensing of biochemical gas with high sensitivity and ultra-short response time, when graphene is regarded as a kind of waveguide, its complex refractive index can also be determined.